Nuclear spin polarization of lactic acid via exchange of parahydrogen-polarized protons

Hyperpolarization has become a powerful tool to enhance the sensitivity of magnetic resonance. A universal tool to hyperpolarize small molecules in solution, however, has not yet emerged. Transferring hyperpolarized, labile protons between molecules is a promising approach towards this end. Therefore, hydrogenative parahydrogen-induced polarization (PHIP) was recently proposed as a source to polarize exchanging protons (PHIP-X). Here, we identified four key components that govern PHIP-X: adding the spin order, polarizing the labile proton, proton exchange, and polarization of the target nucleus. We investigated the last two steps experimentally and using simulations. We found optimal exchange rates and field cycling methods to polarize the target molecules. We also investigated the influence of spin relaxation of exchanging protons on the target polarization. It was found experimentally that transferring the polarization from protons directly bound to the target X-nucleus (here 13C) of lactate and methanol using a pulse sequence was more efficient than applying a corresponding sequence to the labile proton. Furthermore, varying the concentrations of the transfer and target molecules yielded a distinct maximum 13C polarization. We believe this work will further help to understand and optimize PHIP-X towards a broadly applicable hyperpolarization method.

Note that it is possible to adjust the phase such that all LA-peaks show into the same direc9on, as in Fig. 3a of the main manuscript.
Figure S5: Superposi.on of 13 C-NMR spectra of 13 C3-lac.cacid hyperpolarized using PHIP-X.The two corresponding PHIP-X experiments differ in c(1)/c(LA) =3.5 (brown line) and 3.1 (cyan line).   C-NMR spectra of 13 C 3 -lac1c acid hyperpolarized using PHIP-X (magne1c field dependence).Figure S35: 1 H NMR spectrum of methanol hyperpolarized using PHIP-X.The signal of the hyperpolarized methyl group of methanol is located at 2.29 ppm and marked by an arrow.The corresponding signal gain is about 300fold (P=0.1%)compared to the thermal spectrum (figure S36).
Figure S35: 1 H NMR spectrum recorded a`er thermaliza.on of the solu.onwhich was used to hyperpolarize methanol using PHIP-X.The thermal signal of the methyl group of methanol is located at 2.29 ppm and marked by an arrow.
13 C-NMR spectra of hyperpolarized styrene in the presence of methanol.
Figure S36: 13 C NMR spectrum of hyperpolarized styrene in acetone-d6 a`er a PHIP-X.The solu.on contained 13C-methanol to check if there is a polariza.ontransfer from styrene to methanol.All other parameters like pH2pressure were the same as in the PHIP-X experiments containing propargyl alcohol.BPol0 was set to 90 mT.However, no polariza.ontransfer was detected when using phenylacetylene.This is in contrast to the experiments containing propargyl alcohol, where strong 13C polariza.on of methanol was observed.One may interpret this result as a hint that labile protons mediate the polariza.ontransfer in PHIP-X.

Spin dynamics simula1ons.
We analyzed the dependence of the target polariza>ons ( 1 H in Fig. S37b and 13 C in c) for different polariza>on levels of the labile protons (Fig. S37a) and found a linear dependence (Fig. S37).

Figure S10 :
Figure S10: Superposi.on of 13 C-NMR spectra of 13 C3-lac.cacid hyperpolarized using PHIP-X.The three corresponding PHIP-X experiments differ in BPol0 = 5 (brown line), 10 (green line) and 15 (blue line) mT.The resonances at 66.2 ppm and 68.3 ppm were generated by the hyperpolarized 2-13 C nucleus of lac.c acid.The three large resonances at 63.7, 114 and 140 ppm correspond to hyperpolarized allyl alcohol (the transfer agent).

Figure
Figure S17: Superposi.on of 13 C-NMR spectra of 13 C3-lac.cacid hyperpolarized using PHIP-X.The three corresponding PHIP-X experiments differ in BPol0 = 65 (brown line), 70 (green line) and 75 (blue line) mT.The resonances at 63.0, 66.2, 68.3 and 71.5 ppm were generated by the hyperpolarized 2-13 C nucleus of lac.c acid.The strong resonance at 63.7 was generated by hyperpolarized allyl alcohol (the transfer agent).

Figure
Figure S21: 13 C-NMR spectrum of thermal lac.c acid.The spectrum was recorded using the same parameter as applied for the PHIP-X experiments (DEPT, 145 Hz), but with 1,000 scans instead of 1 scan.The resonances at 63.0, 66.2, 68.3 and 71.5 ppm were generated by the 2-13 C nucleus of thermal lac.c acid.The two resonances around 20 ppm were generated by the 3-13 C nucleus of thermal lac.c acid.

Figure
Figure S22: 13 C-NMR spectrum of thermal lac.c acid.The spectrum was recorded using the same parameter as applied for the PHIP-X experiments (DEPT, 145 Hz), but with 1,000 scans instead of 1 scan.The resonances at 63.0, 66.2, 68.3 and 71.5 ppm were generated by the 2-13 C nucleus of thermal lac.c acid.

Figure S23 :
Figure S23: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig. 1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol (at 49.77 ppm).Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The resonances at 63.7, 114

Figure
Figure S24: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The resonances at 49.77 Hz were generated by the hyperpolarized 13C-nucleus of methanol.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig. 1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol.Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The PHIP-X experiment was carried out at BPol0 = 15 mT.

Figure S25 :
Figure S25: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig. 1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol (at 49.77 ppm).Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The resonances at 63.7, 114 and 140 ppm were generated by hyperpolarized allyl alcohol.The PHIP-X experiment was carried out at BPol0 = 30 mT.

Figure S26 :
Figure S26: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The resonances at 49.77 Hz were generated by the hyperpolarized 13C-nucleus of methanol.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig. 1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol.Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The PHIP-X experiment was carried out at BPol0 = 30 mT.

Figure S27 :
Figure S27: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig. 1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol (at 49.77 ppm).Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The resonances at 63.7, 114 and 140 ppm were generated by hyperpolarized allyl alcohol.The PHIP-X experiment was carried out at BPol0 = 45 mT.

Figure
Figure S28: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The resonances at 49.77 Hz were generated by the hyperpolarized 13C-nucleus of methanol.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig. 1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol.Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The PHIP-X experiment was carried out at BPol0 = 45 mT.

Figure S29 :
Figure S29: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig. 1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol (at 49.77 ppm).Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The resonances at 63.7, 114 and 140 ppm were generated by hyperpolarized allyl alcohol.The PHIP-X experiment was carried out at BPol0 = 60 mT.

Figure S30 :
Figure S30: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The resonances at 49.77 Hz were generated by the hyperpolarized 13C-nucleus of methanol.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig. 1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol.Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The PHIP-X experiment was carried out at BPol0 = 60 mT.

Figure S31 :
Figure S31: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig. 1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol (at 49.77 ppm).Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The resonances at 63.7, 114 and 140 ppm were generated by hyperpolarized allyl alcohol.The PHIP-X experiment was carried out at BPol0 = 75 mT.

Figure
Figure S32: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The resonances at 49.77 Hz were generated by the hyperpolarized 13C-nucleus of methanol.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig. 1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol.Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The PHIP-X experiment was carried out at BPol0 = 75 mT.

Figure S33 :
Figure S33: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig. 1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol (at 49.77 ppm).Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The resonances at 63.7, 114 and 140 ppm were generated by hyperpolarized allyl alcohol.The PHIP-X experiment was carried out at BPol0 = 90 mT.

Figure
FigureS34: Superposi.on of two 13 C-NMR spectra of 13 C-methanol hyperpolarized using PHIP-X.The resonances at 49.77 Hz were generated by the hyperpolarized 13C-nucleus of methanol.The thermal reference was recorded 30 minutes a`er the PHIP-X experiment using the same sample.The spectrum of the thermal reference is enlarged by a factor of 10 and recorded using 200 scans.The corresponding PHIP-X experiments differ in the pathways (D1 and D2 in fig.1, main manuscript) how the polariza.onis transferred from the transfer agent (allyl alcohol) to the target 13 C-nucleus of methanol.Path 1 (brown line) provided stronger polariza.onyields and was selected by applying 139 Hz in the DEPT sequence.Path 2 (brown line) was selected by applying 3 Hz in the DEPT sequence.The PHIP-X experiment was carried out at BPol0 = 90 mT.